1. Field of the Invention
This invention relates to the fabrication of a perpendicular magnetic recording (PMR) write head whose main pole is at least partially surrounded by shields formed of magnetic material. In particular it relates to such a head that is shielded at its sides by shields that are non-conformal to the shape of the main pole.
2. Description of the Related Art
The increasing need for high recording area densities (up to 500 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head).
By means of fringing magnetic fields that extend between two emerging pole pieces, longitudinal recording heads form small magnetic domains within the surface plane of the magnetic medium (hard disk). As recorded area densities increase, these domains must correspondingly decrease in size, eventually permitting destabilizing thermal effects to become stronger than the magnetic interactions that tend to stabilize the domain formations. This occurrence is the so-called superparamagnetic limit. Recording media that accept perpendicular magnetic recording, allow domain structures to be formed within a magnetic layer, perpendicular to the disk surface, while a soft magnetic underlayer (SUL) formed beneath the magnetic layer acts as a stabilizing influence on these perpendicular domain structures. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to a disk surface, when used in conjunction with such perpendicular recording media, is able to produce a stable recording with a much higher area density than is possible using standard longitudinal recording.
Since their first use, the PMR head has evolved through several generations. Initially, the PMR head was a monopole, but that design was replaced by a shielded head design with a trailing edge shield (TS), which provides a high field gradient in the down-track direction to facilitate recording at high linear densities. Side shields (SS) then began to be used in conjunction with the trailing edge shields, because it was necessary to eliminate the fringing side fields in order to increase writing density still further. To further reduce the fringing in the down-track direction, thus reducing the length of the write bubble down the track and improving write performance at a skew angle, an optional leading edge shield (LS) was also proposed, making the write head four-side shielded.
Referring to FIG. 1a, there is shown an ABS (air bearing surface) planar view of a prior art PMR writer with a main pole (10) shielded in a (partial) wrap-around manner by a shield (20) that has two symmetrically disposed side portions (30) (hereinafter called a side shield (SS)) and a trailing edge portion (40) (hereinafter called a trailing shield (TS)). Note that a horizontal dashed line (75) indicates an imaginary boundary between the upper portion of the shield that may be considered the trailing edge portion (40) and the two laterally disposed portions (30), continuous with the trailing edge portion (40), taken together, will be considered the side shield (SS). The trailing shield (TS) (40) provides a down-track field gradient for improved writing at higher areal density and the side shield (SS) restricts the fringing of the magnetic field, thereby improving the adjacent track erasure (ATE) performance. Typically a write gap material (59) fills the space between TS and main pole.
As can be seen in this ABS view, the inner edges (31) of SS are shaped to be conformal with the sides (11) of the main pole, producing a generally uniform gap (50) between the inner edges of the shields and the lateral sides (11) (outer surfaces) of the main pole. For simplicity, we shall call such a shield configuration “conformal to the main pole”, symbolized iSS.
Conformality is here (and hereinafter) meant to indicate the fact that when viewed in the ABS plane, edges or edge portions (31) of the inner surface of the shield (its inner periphery) have the same shape as the outer edges of the main pole and are typically parallel to, but displaced from the pole itself so as to produce a uniform spacing between the pole and the shield. A non-conformal portion of the shield would encompass a portion of its inner edge (inner periphery) that is not of a similar shape to that of the pole, that is displaced from the pole in a horizontal (or vertical) direction and, therefore, is characterized by a non-uniform spacing between the shield inner periphery and the outer edges of the pole.
Referring next to FIG. 1b, there is shown an ABS (air bearing surface) view of a prior art PMR writer with a main pole (10) partially shielded in a wrap-around manner by a shield (25) that has a symmetrically disposed side shield (SS) portion (35) and a trailing edge portion (40) (hereinafter called a trailing shield (TS)). Note that a horizontal dashed line (75) indicates the imaginary boundary between the portion of the shield that may be considered the TS (40) and the laterally disposed portions (35) that, taken together, may be considered the SS. Unlike the shield configuration of FIG. 1a, this configuration has a side shield that is not conformal to the main pole, producing generally non-uniform side gaps (55a, 55b). We shall describe such a shield as being “non-conformal to the main pole,” symbolized NCiSS. The NCiSS structure produces a higher strength field than the iSS structure, whereas the iSS structure has less side fringing due to the closeness of the side shields.
An additional issue with the NCiSS is that the shape of the SS is defined by a separate photo-mask process after the main pole shaping process has occurred. Due to the difficulty in aligning two separate masks, the left and right side gaps (55a) and (55b), will generally not be symmetric. The iSS configuration does not have this problem because the SS are self-aligned with the main pole allowing an atomic layer deposition (ALD) process to create a symmetric gap.
It is therefore the object of this invention to address the issues caused by shield asymmetries and non-uniformities and their effect on on-track and off-track performance.
Issues relevant to shield materials are described in the prior arts. For example, Terris et al. (U.S. Pat. No. 7,068,453) discloses side and trailing shields formed of a soft magnetic material.
Gao et al. (U.S. Pat. No. 7,441,325) discloses a trailing shield formed of NiFe.
Nix et al. (U.S. Pat. No. 7,367,112) teaches the formation of a main pole with trailing and side shields.
Guan et al. (U.S. Pat. No. 7,322,095, assigned to the present assignee) teaches a wrap-around shield, as do Jiang et al. (US Patent Application 2009/0154026) and Hsiao et al. (US Patent Application 2009/0154019).
Sasaki et al. (U.S. Pat. No. 7,558,020) discloses a trench etched in alumina and filled with a magnetic layer to form the main pole.
Han et al. (US Patent Application 2009/0091862) teaches conformal side shields around the main pole. This Application is assigned to the same assignee as the present invention.
Zhou et al. (US Patent Application 2009/0052092) teaches that the insulating layer through which the main pole is etched can be alumina or silicon dioxide. This Application is assigned to the same assignee as the present invention.
None of the prior art cited above address the problem addressed by the present invention nor do they disclose the structures and materials of the present invention.